The present disclosure relates to estimating capacitance of capacitors used in power electronic systems.
Modem power electronic systems, such as uninterruptible power supplies (UPSs), use switched converters coupled with LC filters to remove high-frequency components. Alternating current (AC) power capacitors are a major component of these filters. The limited life of a power capacitor usually requires preventive maintenance. Conventionally, timing for preventive maintenance for a power capacitor is estimated based on the stress imposed upon the capacitor, such as voltage, current, and temperature. Although estimating capacitor life in this way generally may be accurate, some power capacitors may contain unexpected defects or may age more quickly than most. Since the total capacitance of each phase of an AC power capacitor bank typically includes several capacitors connected in parallel, it is possible that at least one capacitor could have such a defect. As such, estimating capacitor life according to conventional techniques might inaccurately gauge when preventive maintenance should be scheduled. If proper preventive maintenance is not carried out—or if one capacitor malfunctions unexpectedly—there could be a high risk of failure of the power electronic equipment.